Have you tried:
– deactivating all plugins to see if this resolves the problem. If this works, re-activate the plugins one by one until you find the problematic plugin(s).
– switching to the unedited WP default Twenty Twelve theme to rule out any theme-specific problems.
– resetting the plugins folder by FTP or PhpMyAdmin. Sometimes, an apparently inactive plugin can still cause problems.
– re-uploading all files & folders – except the wp-content folder – from a fresh download of WordPress. Make sure that you delete the old copies of files & folder before uploading the new ones.
– if the above steps don’t help, check your site’s error logs for a more specific error message. If you need help locating them, ask your hosting provider to help you with that.
